What is a hash function?

A hash function is a mathematical algorithm that converts input data of any size into a fixed-size string of characters. It's a one-way function, meaning you can't reverse the process to get the original data from the hash.

What are the differences between hash algorithms?

• MD5 (128-bit): Fast but cryptographically broken. Use only for checksums, not security.
• SHA-1 (160-bit): Deprecated for security use. Vulnerable to collision attacks.
• SHA-256 (256-bit): Current standard for most applications. Secure and widely supported.
• SHA-512 (512-bit): Stronger than SHA-256, used for high-security applications.

What is collision resistance?

Collision resistance means it's computationally infeasible to find two different inputs that produce the same hash output. MD5 and SHA-1 are no longer collision-resistant, while SHA-256 and SHA-512 remain secure.

Common use cases for hashing:

• Password storage (with salt)
• File integrity verification
• Digital signatures
• Blockchain and cryptocurrencies
• Data deduplication
• Checksums for downloads

Is hashing the same as encryption?

No. Encryption is reversible with the right key, while hashing is a one-way function. Hashing is used for verification and integrity, while encryption is used for confidentiality.

Why do different inputs sometimes produce similar-looking hashes?

Hash functions are designed to produce uniformly distributed outputs. Even a tiny change in input creates a completely different hash (avalanche effect), but the outputs may coincidentally share some characters.